1. Field of Invention
The present invention relates to a shock-absorbing device. More particularly, the present invention relates to a shock-absorbing device for protecting a notebook computer module.
2. Description of Related Art
As the level of semiconductor integration continues to increase, size of various electronic devices inside a silicon chip becomes smaller. Therefore, the electronic devices need to be carefully protected from damage. In general, a component having a large number of devices is more vulnerable to physical damage than a component having few devices inside. Therefore, a compact component demands more protection.
Using the central processing unit (CPU) of a notebook computer as an example, the limited volume inside a notebook computer demands a CPU that is slightly different from a CPU installed inside a desktop computer. In addition, due to limited air space inside the notebook computer, airflow inside the notebook computer is also restricted. Therefore, heat dissipation is a problem for the CPU inside a notebook computer as well.
FIG. 1 is a schematic, cross-sectional view of a conventional shock-absorbing device around a notebook computer module. As shown in FIG. 1, a silicon chip 10 is mounted onto a printed circuit board (PCB) 12 via a connector (not shown). Alternatively, the silicon chip 10 is mounted directly onto the PCB 12. In. general, a silicon chip installed inside a notebook computer has limited tolerance for temperature, pressure and bending. Because of the poor heat dissipating capability of the chip 10 alone and the vulnerability of the notebook computer to impact while being carried, a protective device is formed behind the printed circuit board 12 and above the chip 10.
Corresponding in position to chip 10, there is a backing plate 14 attached to the other side of the printed circuit board 12. Because the silicon chip 10 usually has a large number of pins that need to be connected to the printed circuit board 12, the printed circuit board 12 must have a certain degree of planarity to achieve connection. Since most printed circuit boards are not stiff enough, the supporting plate 14 serves as a stiff backing. In addition, the supporting plate 14 also provides some protection against bending to the PCB 12, because any bending is likely to damage the chip 10.
Due to the high level of integration on the silicon chip 10, the amount of heat generated during operation is enormous. Hence, there is a cooling/protective plate 16 on top of the silicon chip 10. The cooling/protective plate 16 is placed over the silicon chip 10 and fixed onto the printed circuit board 12 by a set of screws 18. A protruding element 19 above the chip 10 presses against a surface of the cooling/protective plate 16 so that heat generated by the chip 10 can be conducted away quickly. The cooling/protective plate 16 further has an elastic portion 15 that permits the absorption of shock from external impact. However, how to make the cooling/protective plate 16 contact the chip 10 so that heat can be dissipated without exerting too much pressure on the chip 10 itself is a major design consideration. In general, the cooling/protective plate 16 can only absorb forces in one direction. For example, the cooling/protective plate 16 can absorb a force coming from the top of the chip 10, but cannot withstand a force from the opposite direction. Therefore, the screws must be tightened very carefully so that the cooling/protective plate can exert a correct amount of pressure on the chip 10. The maximum pressure a silicon chip such as a micro-pin grid array (.mu.PGA) can tolerate is only about 689 kpa. Due to unevenness of the chip's surface, stress on the silicon chip may exceed the 689 kpa limit in some local areas. Yet, if insufficient torque is applied to the screws 18, pressure exerted by the cooling/protective plate 16 on the protruding element 19 of the chip 10 is likely to be too low to provide a good contact for cooling. In addition, vibrations caused by physical impact of the notebook computer may loosen the grip of the cooling/protective plate. Even without any external impact, the pre-loaded pressure provided by the screws 18 just for holding the cooling/protective plate 16 onto the printed circuit board 12 is likely to bring down the shock buffering capacity of the cooling/protective plate 16.